Register errors can occur when printing, in a positionally correct manner, from several serially-positioned printing formes, and particularly in the course of color printing. In this case, the web of material passes successively through several printing groups, in which groups the web is imprinted, respectively, in several colors. If these colors are not imprinted exactly on top of, or one after each other in the desired way, because of such variables as a varying module of elasticity of the web of material, a varying tension profile of the web of material, because of climatic influences or because of production tolerances of the printing forme cylinders, this inaccuracy is called register error.
The extent of a register error can be a function of its position in the lateral direction of the web. If this function is imagined as being developed as a Taylor series, it can be seen that, in general, the register error is composed of a term of zero order, which is independent of the lateral position, a term of the first order, which is proportional to the position in the lateral direction, and terms of higher orders. The term of zero order, such as, for example a register error, over the entire width of the web of material, in the transport direction of the web of material, can be corrected, in particular, by a matching of the relative phase positions of the printing cylinders.
DE 199 60 649 A1 describes a device for correcting the lateral position of a web downstream of a dryer. A correction of the color register of the web is not provided by this device.
FIG. 1 of DE 86 10 958 U1 shows a curved lateral extension roller.
DE 83 04 988 U1 discloses a lateral edge control device for a screen printing machine. This device operates in connection with a pivotable roller.
U.S. Pat. No. 4,404,906 A shows a device for controlling the fan-out of a web by the use of a curved roller.
U.S. Pat. No. 6,550,384 B1 describes a device for correcting a width of a web of material. Adjustable deformation elements are looped by the web of material.
U.S. Pat. No. 5,553,542 A discloses a system for the regulation of the width of a web of material by the use of sensors and deformation units.
A rubber blanket with a varied profile for reducing the formation of creases is known from EP 0 659 585 A1.